We've got a few guys locally who are racing the HPI F10 on a small indoor carpet track. They decided to run the cars as they come out of the box with no upgrades. They are keeping this a cost controlled class by limiting cost of servos (Futaba 3003/3004 for example), only allowing the Novak XRS speed control with Orion 2400 lipos, and using Tamiya silver can motors. By keeping this a simple class, the guys are having fun without spending money
The only problem they've run into has been the kit tires really don't work on low traction ozite. A few racers have let them borrow VTA tires, which actually work well and don't look bad on the car. A few racers have also tried the Tamiya F201 "A" compound tires with stock inserts, which also work well. A newer racing is going to try the softer F10 tires once he gets his car built.